In general, an antenna array including a dipole multi-antenna estimates a direction of a received beam by using a phase delay according to an incident angle of the beam. That is, the beam incident into the antenna array generates a predetermined distance delay between the adjacent antennas, and when a gap between the antennas and a phase difference between the antennas are used, it is possible to estimate an incident angle of the received beam. However, in a case of the dipole antenna, a beam pattern heads in an omni-direction, so that there is a disadvantage in that a plurality of antennas needs to be used in order to estimate a direction of the incident beam.
As a method for solving the disadvantage, a directional antenna having a directional beam pattern is used. When the directional antenna is used, it is possible to estimate an incident angle by using size information (for example, power) and beam pattern information about the received beam. However, when the directional antennas are arranged in an array form, beams overlap according to a distance between the antennas, so that there is a problem in that the coupling occurs.